This invention relates to an improvement of a three way switching controller for handling high purity gas, and the like, used in semiconductor manufacturing plants, for example.
The three way switching controller shown in FIGS. 6 and FIG. 7 is an example, of a prior art three way switching controller of this type.
This three way switching controller 50 basically includes a body 56 having: openings 51, 52, and 53; a passage 54 communicating with the openings 51 and 52; a passage 55 communicating with the openings 51 and 53; two normally-closed valves 57 and 58 on the body 56 for opening and closing the passages 54 and 55; and two cylinder/piston mechanisms (herein often referred to only as cylinders) 59 and 60 for opening and closing valves 57 and 58. To openings 51, 52 and 53 (represented by 51a, 52b, and 53c in the diagram of the FIG. 5 for illustrative purposes only) are respectively connected a load (not shown) of a semiconductor manufacturing device (and the like), a source of a first gas A, and a source of a second gas B. Each of the cylinders 59 and 60 is a single acting air cylinder and connected to a source of compressed air by a respective electromagnetic valve, which valves are not shown.
This three way switching controller 50 is designed to cause the valves 57 and 58 to open and close alternately by causing the cylinders 59 and 60 to operate alternately. Namely, when one cylinder 59 is operated to cause the valve 57 thereof to open, operation of the other cylinder 60 is stopped and the valve 58 thereof is allowed to be in its normally closed state. And further, when operation of the one cylinder 59 is stopped, and the valve 57 thereof is allowed to close, the other cylinder 60 is operated and its valve 58 is thereby opened.
However, in a three way switching controller such as this, because both cylinders 59 and 60 are operated simultaneously, both valves 57 and 58 are caused to be opened for a moment and there is a moment when both passages 54 and 55 of the body communicate with one another via passage 51. In other words, when the three way switching controller is switched, lines on the switching sides are connected to each other. Therefore, it has been necessary to prevent both cylinders 59 and 60 from operating simultaneously by shifting the timing of electromagnetic valves which control operation of each cylinder 59 and 60 for supplying the working fluid.
However, in order to provide a time difference for operation of the respective electromagnetic valves, a controller of the electromagnetic vales must be relatively complicated, thereby increasing manufacturing costs of the three way switching controller.
It is an object of the present invention to provide a three way switching controller of simple construction which prevents the lines on the switching sides from being connected to each other at times of switching.